This invention relates to an electronic musical instrument of a type in which harmonic components are digitally combined to form a musical tone and, more particularly, to an electronic musical instrument of the above mentioned type capable of performing a filter function required for characterizing a tone color by digital computation.
A filter used in a prior art digital type electronic musical instrument consists of a memory which digitally stores level information of a slope portion of a filter characteristic. The slope portion means an attenuation region of frequency which is lower than cut-off frequency (in a high-pass filter) or higher than cut-off frequency (in a low-pass filter). Level information stored in the memory is read out in response to information corresponding to frequency. According to this prior art filtering device, the memory must store all level information corresponding to frequencies in the attenuation region so that it must have a large storing capacity. This naturally results in increase in the cost of manufacture. If, for example, required resolution (i.e. minimum unit of the variation steps of attenuation) is 0.75dB and dynamic range of the attenuation is 0-48 dB, the memory must have a storing capacity of 384 bits. If dynamic range increase to 0-72 dB, the required storing capacity increase to 672 bits. If, further, required resolution increases to 0.1875 dB, the required storing capacity increases to 3456 bits. It will be understood from these examples that a memory of a large storing capacity is required if an improved resolution is desired.